Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$93.69	5.136%	$98.5019	$98.50	$98.50	$98.50
Purchase #2	$229.44	8.868%	$249.7867	$249.79	$249.80	$249.80
Purchase #3	$39.45	7.698%	$42.4869	$42.49	$42.50	$42.50
Purchase #4	$50.75	6.609%	$54.1041	$54.10	$54.10	$54.10
Purchase #5	$241.29	4.162%	$251.3325	$251.33	$251.35	$251.30
Purchase #6	$159.40	4.371%	$166.3674	$166.37	$166.35	$166.40
Purchase #7	$151.32	3.257%	$156.2485	$156.25	$156.25	$156.20
7 purchase totals =	$965.34		$1,018.8280	$1,018.83	$1,018.85	$1,018.80